In a typical cellular radio system, wireless terminals, also known as mobile stations and/or user equipment units (UEs), communicate via a radio access network (RAN) to one or more core networks. The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell is also broadcasted in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity.
Mobile telecommunications systems are normally statically configured with a parameter set defining the behavior of the system. The systems are based on standards which define radio bearers to carry traffic with different characteristics, e.g. speech, streaming video, or packet data. Standards such as the 3GPP standards referenced above also define different UE/RRC states. See, for example chapter 7 in 3GPP TS 25.331 V10.4.0 (2011-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol specification (Release 10), incorporated herein by reference, which describes states such as CELL_DCH state, CELL_FACH state, CELL_PCH state, URA_PCH state, and the Idle state. These names of these states are understood in view of the following channels/areas: Dedicated Channel (DCH); Forward Access Channel (FACH); Random Access Channel (RACH); Paging Channel (PCH); UTRAN registration area (URA).
For each wireless terminal in the connected mode, a node of the radio access network, such as a radio network controller (RNC) node, determines in which of these states the wireless terminal operates. Whichever of the UE/RRC states a wireless terminal currently is in has consequences which affect, e.g., the UE battery consumption and the resource consumption in the mobile network.
For UTRAN (WCDMA) in particular the 3GPP standard defines the Radio Access Bearer (RAB) to carry the services, where the Interactive RAB is specified for best effort traffic. The 3GPP standard also defines UE/RRC states such as CELL_DCH, CELL_FACH, CELL_PCH, and URA_PCH, mentioned above.
Packet data services have escalated, particularly with the introduction of wireless terminals in the form of devices such as Smartphones, and with personal computers (PCs) now widely participating in the mobile networks. Most of the packet traffic is based on the internet protocol (IP), e.g., internet services, and is normally treated as best effort traffic in the mobile network. Internet services are of many types and different characteristics, e.g. web browsing, chat, email, file sharing, and video streaming.
Within an Internet Protocol (IP) flow there are typically times of activity and times of inactivity. Periods of activity will be separated by times of inactivity of different length. Within the IP flow, a burst can for example be defined by IP packets arriving with a maximum inter-arrival time (IATmax). The Idle Time Between bursts (ITB) is defined as the time between the last packet in one burst and the first packet of the next burst.
As mentioned above, a radio access network node such as the radio network controller keeps track of the UE/RRC state in which a wireless terminal is currently operating and also governs the transition of the wireless terminal between UE/RRC states. In other words, the radio network controller determines when a wireless terminal should transition from one UE/RRC state, such as the CELL_DCH state, to another state, such as the URA_PCH state, for example. Parameters to govern the transition between UE/RRC states are normally timer based. FIG. 1 generally depicts that, when switching from a higher more resource consuming state to a lower less resource consuming state, a wireless terminal may be required to transition from one UE/RRC state to another UE/RRC state upon expiration of a timer. The timer may be activated or initiated by some UE-related network activity, e.g. forwarding of an IP packet to/from the UE. The timer may expire due to some UE-related inactivity, e.g., no IP packet forwarded to/from the UE. Expiration of the timer may prompt the transition from one UE/RRC state to another UE/RRC state. Transfer to a state of higher activity is normally transmission-triggered, e.g., by the filling of a buffer.
There are problems with existing ways of governing transitions between the UE/RRC states. For example, legacy solutions govern the transition between UE/RRC states essentially statically, e.g., using fixed timer values, and therefore do not adapt the timers or the transitions according to the characteristics of the data flow. Such static setting does not allow cost optimal decisions for transferring between UE/RRC states, nor does it allow for adapting the cost optimal decision point to the load situation in the network. Such static setting results in suboptimal operation with regard to parameters such as UE battery consumption and network resource consumption. These problems have been particularly accentuated in UTRAN with the increasing amount of bursty packet data traffic in mobile networks generating a high control plane load due to frequent state transitions.
Furthermore, when a wireless terminal in UTRAN finishes data transmission/reception in the CELL_DCH state, after a shorter period of inactivity the wireless terminal is switched down to the CELL_FACH state, and after another period of inactivity the wireless terminal is further switched down, e.g., to URA_PCH state or IDLE. There are several problems with this approach.
As one such problem, CELL_FACH is used as a transient state, which means that wireless terminals are switched down to this state due to inactivity and not because they have data with characteristics suitable to transmit in this state. These wireless terminals will either be switched up to CELL_DCH again when a data burst arrives or, if no data transmission takes place, the wireless terminals are switched down further. Both change of a UE/RRC state and residing in a UE/RRC state contributes to the load on the network, e.g., on the radio network controller (RNC). Inefficient state switching thus increases the RNC load.
As another such problem, low rate services may also occupy unnecessary network resources if residing on CELL_DCH when CELL_FACH is a more efficient state.